The usage pattern for widen_imprecise_scalars() looks as follows:
prev_st = find_prev_entry(env, ...);
queued_st = push_stack(...);
widen_imprecise_scalars(env, prev_st, queued_st);
Where prev_st is an ancestor of the queued_st in the explored states
tree. This ancestor is not guaranteed to have same allocated stack
depth as queued_st. E.g. in the following case:
def main():
for i in 1..2:
foo(i) // same callsite, differnt param
def foo(i):
if i == 1:
use 128 bytes of stack
iterator based loop
Here, for a second 'foo' call prev_st->allocated_stack is 128,
while queued_st->allocated_stack is much smaller.
widen_imprecise_scalars() needs to take this into account and avoid
accessing bpf_verifier_state->frame[*]->stack out of bounds.
Fixes: 2793a8b015f7 ("bpf: exact states comparison for iterator convergence checks")
Reported-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20251114025730.772723-1-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
b0c8e6d3d8